The present invention relates to a desulfurization-denitration apparatus for exhaust gas, and particularly relates to a desulfurization-denitration apparatus (hereinafter referred to as “dry desulfurization apparatus”) for exhaust gas that is applied in an exhaust gas processing apparatus using a particulate carbonaceous adsorbent (hereinafter referred to as “adsorbent”) and provided to equipment such as a boiler, sintering device, refuse incinerator, or the like that generates exhaust gas containing SO2 gas and/or NOx, HCl, HF, Hg (hereinafter referred to as “harmful substances in exhaust gas”) and other harmful gases.
A dry desulfurization-denitration apparatus is composed of a desulfurization tower (adsorption tower) for adsorbing and removing harmful substances in the exhaust gas onto an adsorbent; a regeneration tower for heating and regenerating the adsorbent onto which the harmful substances are adsorbed; and a conveyance device for recirculating and conveying the adsorbent between the desulfurization tower and the regeneration tower. The adsorbent in the desulfurization tower comes in contact with the exhaust gas and adsorbs or decomposes the harmful substances in the exhaust gas while slowly descending from top to bottom. At the same time, dust in the exhaust gas is also collected by the filtering effects of the particulate adsorbent.
In order for the harmful substances or dust to be removed with consistently high efficiency, the adsorbent must flow downward at a uniform speed in the horizontal cross-section of the moving bed thereof. The adsorbent also generates heat of adsorption when adsorbing the harmful substances.
The generated heat of adsorption is usually carried off by the sensible heat of the exhaust gas passing through the adsorbent, and by the sensible heat of the adsorbent that is discharged from the desulfurization tower, but in locations where transfer of the adsorbent is stagnated, or in locations where the exhaust gas does not pass through with adequate speed, the amount of the generated heat exceeds that of the heat carried off, the temperature of adsorbent increases, and heat storage occurs, and when such heat storage occurs, the carbonaceous adsorbent can sometimes develop hot spots or ignite.
In the conventional dry desulfurization apparatus, various types of adsorbent discharging devices provided to the bottom of the desulfurization tower are designed in order to maintain high-efficiency removal of harmful substances or dust, and to prevent ignition or the occurrence of hot spots.
FIGS. 6 and 7 show examples of the structure of the desulfurization-denitration tower of a dry desulfurization apparatus in actual operation. The desulfurization-denitration apparatus shown in FIGS. 6 and 7 is provided with a hollow tower body 1, and an entrance part 2 and an exit part 3 for the exhaust gas X are provided to opposing front and rear side walls 1a, 1b, respectively, of the tower body 1.
An entrance louver 4 and an exit louver 5 are provided at a predetermined spacing at the center of the tower body 1, and an adsorbent A is packed between the louvers 4, 5. The adsorbent A is fed from the top end of the tower body 1, and a device 6 for discharging the adsorbent A is provided to the bottom end part of the tower body 1. In the example shown in FIG. 6, the discharging device 6 is composed of a belt conveyor.
The adsorbent A moves slowly downward in a packed state between the louvers 4, 5 according to the amount of discharging of the discharging device 6, and during this movement, the exhaust gas X flows sideways through the packed moving bed of the adsorbent A and thus comes in contact therewith, so that harmful substances are adsorbed thereon.
The desulfurization-denitration apparatus shown in FIG. 6 has a structure in which a middle louver 7 is provided between the entrance louver 4 and the exit louver 5, and the adsorbent A between the entrance louver 4 and the middle louver 7 (hereinafter referred to as “front chamber”) moves at a speed that is different from that of the adsorbent A between the middle louver 7 and the exit louver 5 (hereinafter referred to as “rear chamber”).
A throttle portion 8 that closes in an inverted square pyramid shape is formed above the discharging device 6, and partitions 9, the spacing between which is adjusted, are provided inside the throttle portion 8 so that the adsorbent A moves at a uniform speed through the packed bed above. As shown in the top view of FIG. 7, a plurality of partitions 9 is assembled in the X and Y directions so as to divide the inside of the throttle portion 8 into a grid.
However, in a structure such as the one described above, when the width of the throttle portion 8 in the X direction is too large in relation to the width of the belt conveyor that constitutes the discharging device 6, not only does the height of the throttle portion 8 increase, but numerous partitions 9 are needed, and the structure becomes complex.
Fabrication is therefore made difficult by the reduced spacing between the partitions 9 near the bottom end of the throttle portion 8, and movement of the adsorbent A can be stagnated by friction from the wall surfaces at the corners where the partitions 9 intersect in the X direction and Y direction.
Patent Document 1 proposes a desulfurization-denitration apparatus that is structured as shown in FIGS. 8 and 9. The desulfurization tower shown in these drawings has a tower body 1, entrance and exit parts 2, 3 for exhaust gas X, entrance and exit louvers 4, 5, a middle louver 7, and an exit hood part 10. Since the configuration of these components is essentially the same as in the conventional example shown in FIGS. 6 and 7, the same reference symbols are used to refer to portions that correspond to or are the same as in the conventional example, and no redundant description thereof will be given. Only the characteristic aspects will be described.
In this conventional desulfurization-denitration apparatus, the discharging devices 6a are composed of roll feeders, three of which being employed. The width of each of the discharging devices 6a in the X direction is substantially the same as the width of the portion in which the adsorbent A is packed, and the discharging speed in the X direction is thereby made uniform.
The three discharging devices 6a are arranged in the Y direction, and the thickness handled by each discharging device 6a is reduced. A throttle portion 8a for feeding the adsorbent A to the discharging devices 6a is provided with a side wall formed in a rectangular shape, and a plurality of partitions 9a provided inside the throttle portion 8a. 
Discharging ports 9b opened at the top ends of the discharging devices 6a are structured so that one wall surface (partitions 9a or the side wall of the throttle portion 8a) thereof is vertical, and the adsorbent A moves at a uniform speed without stagnant regions forming.
In the desulfurization-denitration apparatus configured as shown in FIGS. 8 and 9, since a plurality of partitions 9 is not arranged in a grid in the throttle portion 8 as in the conventional example shown in FIGS. 6 and 7, the problems of structural complexity and difficulty of manufacture can be overcome. However, the conventional apparatus described above has the technical drawbacks described below.    Patent Document 1: Japanese Laid-open Patent Publication No. 2006-15281